1. Field of the Invention
The present invention relates to an endoscopic treatment instrument. Priority is claimed on Japanese Patent Application No. 2006-257351, filed Sep. 22, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
With respect to early-stage cancer of the stomach or esophagus, an endoscopic demucosation is performed in which a mucosa in an ailing or affected area is excised by using a frequency snare introduced into a body cavity through a channel of the endoscope. In such a demucosational operation, an endoscopic treatment instrument is used which includes a generally cylindrical transparent cap that is fitted over the tip of an insertion section of the endoscope.
In an operation with the use of this endoscopic treatment instrument, a snare wire of the high frequency snare is firstly extended radially in the transparent cap and then a mucosa to be excised is absorbed so as to form the shape of a polyp in the transparent cap while the snare wire is extended as it is. Thereafter, a base portion of the polyp-shaped mucosa is excised by the use of the frequency snare. At this time, it is necessary for the snare wire to be precisely placed on the base portion of the polyp-shaped mucosa drawn in the transparent cap. To this end, there is a proposal in which a hooked portion is provided on the tip of the transparent cap and the snare wire is extended along the hooked portion and retained as it is. See, e.g., Japanese Unexamined Patent Application, First Publication Nos. 2002-45369 and 2004-230054.
With the above-described conventional endoscopic treatment instrument, it is impossible to extend the snare wire in the transparent cap while maintaining the transparent cap in a floating state or so as to be untouched. Namely, when the snare wire is extended, the transparent cap is inevitably pressed against tissues or mucosa. As such, the transparent cap is firstly pressed against a normal area or tissue and the snare wire is then projected through a treatment tool insertion channel. At this time, the affected area necessarily goes out of view of the endoscope. So, it takes a lot of time and trouble to find the affected area again for excising the polyp thereof. Furthermore, a lot of skill is necessary to speed up a pre-looping operation in which the snare wire is extended (or a loop of the snare wire is widened) in the transparent cap. Furthermore, since the snare wire is forwardly and rearwardly moved through the treatment tool insertion channel of the insertion section, it is necessary to pull out the treatment tool concerned in order to replace it with another treatment tool such as an injection needle and the like.